Absorbent core with high superabsorbent material content

ABSTRACT

An absorbent core includes a core wrap enclosing an absorbent material, and one or more channels extending at least in the crotch region. The core wrap is at least partially sealed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Nonprovisional applicationSer. No. 15/627,494, filed on Jun. 20, 2017, which is a continuation ofU.S. Nonprovisional application Ser. No. 14/100,062, filed on Dec. 9,2013, which is a continuation of European Application No. 12196343.3,filed on Dec. 10, 2012, the entirety of which is incorporated byreference herein.

FIELD OF THE INVENTION

The invention is for an absorbent core for personal hygiene absorbentproducts such as, but not limited to, baby diapers, training pants,feminine pads or adult incontinence products.

BACKGROUND OF THE INVENTION

Absorbent articles for personal hygiene, such as disposable diapers forinfants, training pants for toddlers or adult incontinenceundergarments, are designed to absorb and contain body exudates, inparticular large quantity of urine. These absorbent articles compriseseveral layers providing different functions, for example a topsheet, abacksheet and in-between an absorbent core, among other layers.

The function of the absorbent core is to absorb and retain the exudatesfor a prolonged amount of time, for example overnight for a diaper,minimize re-wet to keep the wearer dry and avoid soiling of clothes orbed sheets. The majority of currently marketed absorbent articlescomprise as absorbent material a blend of comminuted wood pulp withsuperabsorbent polymers (SAP) in particulate form, also called absorbentgelling materials (AGM), see for example U.S. Pat. No. 5,151,092(Buell). Absorbent articles having a core consisting essentially of SAPas absorbent material (so called “airfelt-free” cores) have also beenproposed but are less common than traditional mixed cores (see e.g.WO2008/155699 (Hundorf), WO95/11652 (Tanzer), WO2012/052172 (VanMalderen)).

Absorbent articles comprising an absorbent core with slits or grooveshave also been proposed, typically to increase the fluid acquisitionproperties of the core or to act as a folding guide. WO95/11652 (Tanzer)discloses absorbent articles which include superabsorbent materiallocated in discrete pockets having water-sensitive and water-insensitivecontainment structure. WO2009/047596 (Wright) discloses an absorbentarticle with a slit absorbent core.

Absorbent products which are flexible in the crotch region provide thebenefits of improved freedom of movement for the wearer, especially whenthe user's legs compress the crotch region of the article laterally.However the inventors have found that highly flexible products may ingenerally have a poor resiliency when becoming wet, and thus tend tolose their shape when compressed by the movement of the wearer's legs.As the absorbent core is deformed, the product can fail performingproperly and this increases the chance of failure such as fluidleakages. The inventors have now found a new absorbent core structurewhich can provide the benefit of good flexibility combined with goodresiliency when loaded with fluid.

SUMMARY OF THE INVENTION

The invention is for an absorbent core as defined in the claims and anabsorbent article comprising this absorbent core. The absorbent corecomprises a core wrap enclosing an absorbent material, wherein theabsorbent material may comprise at least 80% of superabsorbent polymers(“SAP”) by weight of the absorbent material. The absorbent corecomprises a front edge, a back edge and two longitudinal edges, and hasa longitudinal axis oriented in a longitudinal direction. The absorbentmaterial comprises at least one channel, which is at least present inthe crotch region and may extend to the front and/or back regions. Theabsorbent core have a Wet Compression Force below 5.00 N, in particularfrom 1.00 to 3.00N, as measured by the WCACF Test.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of an absorbent article in the form of a diapercomprising an exemplary absorbent core according to the invention;

FIG. 2 is a transversal cross-section of the diaper of FIG. 1;

FIG. 3 is a top view of the exemplary absorbent core of the diaper ofFIG. 1 taken in isolation;

FIG. 4 is a transversal cross-section of the core of FIG. 3;

FIG. 5 is a longitudinal cross-section of the core of FIG. 3;

FIG. 6 shows a top view of an alternative absorbent core of theinvention.

FIG. 7 is a schematic description of an apparatus used to carry out theWet Caliper And Compression Force Test, further detailed below.

DETAILED DESCRIPTION OF THE INVENTION Introduction

As used herein, the term “absorbent article” refers to disposableproducts such as infant or adult diapers, training pants, and the likewhich are placed against or in proximity to the body of the wearer toabsorb and contain the various exudates discharged from the body.Typically these articles comprise a topsheet, backsheet, an absorbentcore and optionally an acquisition layer and/or distribution layer andtypically other components, with the absorbent core normally placedbetween the backsheet and the acquisition system or topsheet.

As used herein, the term “absorbent core” refers to an individualcomponent, which is placed or is intended to be placed within anabsorbent article and which comprises an absorbent material enclosed ina core wrap. The term “absorbent core” does not cover an acquisition ordistribution layer or any other component of an absorbent article whichis not either integral part of the core wrap or placed within the corewrap. The absorbent core is typically the component of an absorbentarticle which comprises all, or at least the majority of, superabsorbentparticles (SAP) and has the most absorbent capacity of all thecomponents of the absorbent article.

A “nonwoven web” as used herein means a manufactured sheet, web or battof directionally or randomly orientated fibers, bonded by friction,and/or cohesion and/or adhesion, excluding paper and products which arewoven, knitted, tufted, stitch-bonded incorporating binding yarns orfilaments, or felted by wet-milling, whether or not additionallyneedled. The fibers may be of natural or man-made origin and may bestaple or continuous filaments or be formed in situ. Commerciallyavailable fibers have diameters ranging from less than about 0.001 mm tomore than about 0.2 mm and they come in several different forms such asshort fibers (known as staple, or chopped), continuous single fibers(filaments or monofilaments), untwisted bundles of continuous filaments(tow), and twisted bundles of continuous filaments (yam). Nonwoven webscan be formed by many processes such as meltblowing, spunbonding,solvent spinning, electrospinning, carding and airlaying. The basisweight of nonwoven webs is usually expressed in grams per square meter(g/m² or gsm).

“Comprise,” “comprising,” and “comprises” are open ended terms, eachspecifies the presence of the feature that follows, e.g. a component,but does not preclude the presence of other features, e.g. elements,steps, components known in the art or disclosed herein. These termsbased on the verb “comprise” should be read as encompassing the narrowerterms “consisting essential of” which excludes any element, step oringredient not mentioned which materially affect the way the featureperforms its function, and the term “consisting of” which excludes anyelement, step, or ingredient not specified. Any preferred or exemplaryembodiments described below are not limiting the scope of the claims,unless specifically indicated to do so. The words “typically”,“normally”, “advantageously” and the likes also qualify features whichare not intended to limit the scope of the claims unless specificallyindicated to do so.

Unless indicated otherwise, the description refers to the absorbent coreand absorbent article before use (i.e. dry, and not loaded with a fluid)and conditioned at least 24 hours at 21° C.+/−2° C. and 50+/−20%Relative Humidity (RH).

General Description of the Absorbent Article 20

An exemplary absorbent article 20 in which the absorbent core 28 of theinvention can be used is an infant taped diaper 20 as represented inFIG. 1. FIG. 1 is a top plan view of the exemplary diaper 20, in aflat-out state, with portions of the structure being cut-away to moreclearly show the construction of the diaper 20. This diaper 20 is shownfor illustration purpose only as the invention may be used for making awide variety of diapers or other absorbent articles.

The absorbent article 20 comprises a liquid permeable topsheet 24, aliquid impermeable backsheet 25, an absorbent core 28 between thetopsheet 24 and the backsheet 25. The absorbent article may alsocomprise further typical components such as an acquisition layer 52and/or a distribution layer 54 (collectively referred to asacquisition-distribution system “ADS”, designated as 50 in FIG. 2), andelasticized gasketing cuffs 32 present between topsheet and backsheetand upstanding barrier leg cuffs 34, which will be further detailed inthe following. FIGS. 1-2 also show other typical taped diaper componentssuch as a fastening system comprising fastening tabs 42 attached towardsthe back edge 12 of the article and cooperating with a landing zone 44towards the front edge of the article. The absorbent article may alsocomprise other typical components, which are not represented in theFigures, such as a back elastic waist feature, a front elastic waistfeature, transverse barrier cuff(s), a lotion application, etc.

The absorbent article 20 comprises a front edge 10, a back edge 12, andtwo longitudinal edge edges. The front edge 10 is the edge of thearticle which is intended to be placed towards the front of the userwhen worn, and the back edge 12 is the opposite edge. The absorbentarticle may be notionally divided by a longitudinal axis 80 extendingfrom the front edge to the back edge of the article and dividing thearticle in two substantially symmetrical halves relative to this axis,when viewing the article from the wearer facing side in a flat outconfiguration, as exemplarily shown in FIG. 1. If some part of thearticle is under tension due to elasticized components, the article maybe typically flattened using clamps along the periphery of the articleand/or a sticky surface, so that the topsheet and backsheet can bepulled taut so as to be substantially flat. The absorbent article 20 canalso be notionally divided by a transversal axis 90 in a front regionand a back region of equal length measured on the longitudinal axis,when the article is in such a flat state. This article's transversalaxis 90 is perpendicular to the longitudinal axis 80 and placed at halfthe length of the article. The length of the article can be measuredalong the longitudinal axis 80 from front edge 10 to back edge 12.

The topsheet 24, the backsheet 25, the absorbent core 28 and the otherarticle components may be assembled in a variety of well knownconfigurations, in particular by gluing and/or heat embossing. Exemplarydiaper assemblies are for example generally described in U.S. Pat. Nos.3,860,003, 5,221,274, 5,554,145, 5,569,234, 5,580,411, and 6,004,306.The absorbent article is preferably thin. The article may beadvantageously thin at the intersection of the longitudinal andtransversal axis, for example with a caliper of from 1.0 mm to 8.0 mm,in particular from 1.5 mm to 6.0 mm, as measured using the AbsorbentArticle Caliper Test described below.

These and other components of the articles will now be discussed in moredetails.

Absorbent Core 28

The absorbent core of the invention comprises absorbent material with ahigh amount of superabsorbent polymers (herein abbreviated as “SAP”)enclosed within a core wrap. The SAP content represents at least 80% byweight of the absorbent material contained in the core wrap. The corewrap is not considered as absorbent material for the purpose ofassessing the percentage of SAP in the absorbent core. The absorbentmaterial defines an absorbent material deposition area 8 as seen whenthe core is placed substantially flat. As used herein, the term“absorbent core” does not include the topsheet, the backsheet and (ifpresent) an acquisition-distribution system or layer which is notintegral part of the absorbent core, in particular which is not placedwithin the core wrap. The core may consist essentially of, or consistof, the core wrap, the absorbent material and optionally glue. The term“absorbent core” and the term “core” are herein used interchangeably.

The exemplary absorbent core 28 of the absorbent article of FIG. 1 isshown in isolation in FIGS. 3-5. The absorbent core of the inventioncomprises a front edge 280, a back edge 282 and two longitudinal edges284, 286 joining the front edge 280 and the back edge 282. The frontedge 280 of the core is the edge of the core intended to be placedtowards the front edge 10 of the absorbent article. Typically theabsorbent material will be advantageously distributed in higher amounttowards the front edge than towards the back edge as more absorbency isrequired at the front. Typically the front and back edges of the core280, 282 are shorter than the longitudinal edges 284, 286 of the core.The absorbent core may also comprise a top side and a bottom side. Thetop side 288 of the core is the side intended to be placed towards thetopsheet and the bottom side 290 the side intended to be placed towardsthe backsheet in the finished article 20. The top side 288 of the coreis typically more hydrophilic than the bottom side 290. The width of thecore at the crotch point as measured between the two longitudinal edges284,286 should be sufficient for the WCACF Test to be conducted, i.e.should be at least 40 mm. The width of the core at the crotch point mayin particular be of from 45 mm to 200 mm, or from 50 mm to 150 mm.

The absorbent core may be notionally divided by a longitudinal axis 80′extending from the front edge to the back edge of the core and dividingthe core in two substantially symmetrical halves relative to this axis,when viewing the core from the topside in a flat out configuration, asexemplarily shown in FIG. 3. Typically the longitudinal axis 80′ of thecore and the longitudinal axis 80 of the article in which the core isintended to be placed will be contiguous, when viewed from the top as inFIG. 1. The transversal axis of the core (herein also referred to as“crotch line”), is perpendicular to the longitudinal axis and is passingthrough the crotch point C of the core. The crotch point C is the pointof the absorbent core placed at a distance of 0.45 of L from the frontedge of the absorbent core, L being the length of the core as measuredfrom its front edge to its back edge on the longitudinal axis 80′, asillustrated in FIG. 3. The full length L of the core is measured fromthe front edge 280 to the back edge 282 of the core along itslongitudinal axis 80′ and also includes the region of the core wrapwhich does not enclose the absorbent material, in particular at thefront and back end seals when present. The length of the core L is of atleast 320 mm, for example from 320 mm to 600 mm.

The crotch region 81 is defined herein as the region of the coreextending from the crotch line, i.e. at the level of the crotch point C,towards the back edge and front edge of the core by a distance of aquarter of L (L/4) in both directions for a total length of L/2. Thefront region 82 and back region 83 of the core are the remaining regionsof the deposition area towards the front and back edges of the corerespectively.

The core wrap may be formed by two nonwoven material 16, 16′ which maybe at least partially sealed along the edges of the absorbent core. Thecore wrap may be at least partially sealed along the core's front edge,back edge and two longitudinal edges so that substantially no absorbentmaterial leaks out of the absorbent core wrap when performing thecompression step of the WCACF test described below. It is not excludedthat the core wrap can be sealed with a seal line further inboard thanthe core's edge, for example as in a gift wrapping if the core wrapcomprises a single substrate. The absorbent core may also advantageouslyachieve an SAP loss of no more than about 70%, 60%, 50%, 40%, 30%, 20%,10% according to the Wet Immobilization Test described inWO2010/0051166A1. Further aspects of the absorbent core will now bedescribed in further details. The absorbent core of the invention may berelatively thin and thinner than can conventional airfelt cores. Inparticular the caliper of the core (before use) as measured at thecrotch point (C) according to the Core Caliper Test as described hereinmay be from 0.25 mm to 5.0 mm, in particular from 0.5 mm to 4.0 mm.

By “absorbent material” it is meant a material which has at least someabsorbency and/or liquid retaining properties, such as SAP, cellulosicfibers as well as some hydrophilically treated synthetic fibers.Typically, glues used in making absorbent cores have no absorbencyproperties and are not considered as absorbent material. The SAP contentmay be higher than 80%, for example at least 85%, at least 90%, at least95% and even up to and including 100% of the weight of the absorbentmaterial contained within the core wrap. This high SAP content mayprovide a relatively thin core compared to conventional core typicallycomprising between 40-60% SAP and the rest of cellulose fibers. Theabsorbent material of the invention may in particular comprises lessthan 10% weight percent, or less than 5% weight percent, or even besubstantially free of natural and/or synthetic fibers. The absorbentmaterial may advantageously comprise little or no airfelt (cellulosic)fibers, in particular the absorbent core may comprise less than 15%,10%, or 5% airfelt (cellulose) fibers by weight of the absorbent core,or even be substantially free of cellulose fibers.

The absorbent core of the invention may further comprise adhesive forexample to help immobilizing the SAP within the core wrap and/or toensure integrity of the core wrap, in particular when the core wrap ismade of two or more substrates. The core wrap will typically extend to alarger area than strictly needed for containing the absorbent materialwithin.

Cores comprising relatively high amount of SAP with various core designshave been proposed in the past, see for example in U.S. Pat. No.5,599,335 (Goldman), EP1,447,066 (Busam), WO95/11652 (Tanzer),US2008/0312622A1 (Hundorf), WO2012/052172 (Van Malderen). In someembodiments, the absorbent material may be continuously present withinthe core wrap. In this case, the absorbent material may be for exampleobtained by the application of a single continuous layer of absorbentmaterial. In other embodiments, the absorbent material may be comprisedof individual pockets or stripes of absorbent material enclosed withinthe core wrap and separated by junction areas.

The continuous layer of absorbent material, in particular of SAP, mayalso be obtained by combining two “half” absorbent layers havingdiscontinuous absorbent material application pattern wherein theresulting layer is substantially continuously distributed across theabsorbent particulate polymer material area, as taught inUS2008/0312622A1 (Hundorf) for example. The absorbent core 28 may forexample, as illustrated in FIG. 5, comprise a first absorbent layer anda second absorbent layer, the first absorbent layer comprising a firstsubstrate 16 and a first layer 61 of absorbent material, which may be100% SAP, and the second absorbent layer comprising a second substrateand a second layer of absorbent material, which may also be 100% SAP,and a fibrous thermoplastic adhesive material 51 at least partiallybonding each layer of absorbent material 61, 62 to its respectivesubstrate. The first substrate 16 and the second substrate 16′ form thecore wrap. The first and second absorbent layers may be deposited ontheir respective substrate in a deposition pattern comprising land areascomprising absorbent material and junction areas between the land areaswhich are free of absorbent material. The land areas as exemplified inFIG. 5 for example may be for example transversally orientated and spanthe width of the absorbent material deposition area 8. The fibrousthermoplastic adhesive material 51 may be at least partially in contactwith the absorbent material 61, 62 in the land areas and at leastpartially in contact with the substrate layer in the junction areas.This imparts an essentially three-dimensional structure to the fibrouslayer of thermoplastic adhesive material 51, which in itself isessentially a two-dimensional structure of relatively small thickness,as compared to the dimension in length and width directions. Thereby,the fibrous thermoplastic adhesive material may provide cavities tocover the absorbent material in the land area, and thereby immobilizesthis absorbent material, which as already indicated may be 100% SAP.

The thermoplastic adhesive material may comprise, in its entirety, asingle thermoplastic polymer or a blend of thermoplastic polymers,having a softening point, as determined by the ASTM Method D-36-95 “Ringand Ball”, in the range between 50° C. and 300° C., and/or thethermoplastic adhesive material may be a hotmelt adhesive comprising atleast one thermoplastic polymer in combination with other thermoplasticdiluents such as tackifying resins, plasticizers and additives such asantioxidants.

The thermoplastic polymer has typically a molecular weight (Mw) of morethan 10,000 and a glass transition temperature (Tg) usually below roomtemperature or −6° C.<Tg<16° C. Typical concentrations of the polymer ina hotmelt are in the range of about 20 to about 40% by weight. Thethermoplastic polymers may be water insensitive. Exemplary polymers are(styrenic) block copolymers including A-B-A triblock structures, A-Bdiblock structures and (A-B)n radial block copolymer structures whereinthe A blocks are non-elastomeric polymer blocks, typically comprisingpolystyrene, and the B blocks are unsaturated conjugated diene or(partly) hydrogenated versions of such. The B block is typicallyisoprene, butadiene, ethylene/butylene (hydrogenated butadiene),ethylene/propylene (hydrogenated isoprene), and mixtures thereof. Othersuitable thermoplastic polymers that may be employed are metallocenepolyolefins, which are ethylene polymers prepared using single-site ormetallocene catalysts. Therein, at least one comonomer can bepolymerized with ethylene to make a copolymer, terpolymer or higherorder polymer. Also applicable are amorphous polyolefins or amorphouspolyalphaolefins (APAO) which are homopolymers, copolymers orterpolymers of C2 to C8 alpha olefins.

The tackifying resin may exemplarily have a Mw below 5,000 and a Tgusually above room temperature, typical concentrations of the resin in ahotmelt are in the range of about 30 to about 60%, and the plasticizerhas a low Mw of typically less than 1,000 and a Tg below roomtemperature, with a typical concentration of about 0 to about 15%.

The thermoplastic adhesive 51 used for the fibrous layer preferably haselastomeric properties, such that the web formed by the fibers on theSAP layer is able to be stretched as the SAP swell. Exemplaryelastomeric, hotmelt adhesives include thermoplastic elastomers such asethylene vinyl acetates, polyurethanes, polyolefin blends of a hardcomponent (generally a crystalline polyolefin such as polypropylene orpolyethylene) and a Soft component (such as ethylene-propylene rubber);copolyesters such as poly (ethylene terephthalate-co-ethylene azelate);and thermoplastic elastomeric block copolymers having thermoplastic endblocks and rubbery mid blocks designated as A-B-A block copolymers:mixtures of structurally different homopolymers or copolymers, e.g., amixture of polyethylene or polystyrene with an A-B-A block copolymer;mixtures of a thermoplastic elastomer and a low molecular weight resinmodifier, e.g., a mixture of a styrene-isoprenestyrene block copolymerwith polystyrene; and the elastomeric, hot-melt, pressure-sensitiveadhesives described herein. Elastomeric, hot-melt adhesives of thesetypes are described in more detail in U.S. Pat. No. 4,731,066 issued toKorpman on Mar. 15, 1988.

The thermoplastic adhesive material is advantageously applied as fibers.The fibers may exemplarily have an average thickness of about 1 to about50 micrometers or about 1 to about 35 micrometers and an average lengthof about 5 mm to about 50 mm or about 5 mm to about 30 mm. To improvethe adhesion of the thermoplastic adhesive material to the substrate orto any other layer, in particular any other nonwoven layer, such layersmay be pre-treated with an auxiliary adhesive. The fibers adhere to eachother to form a fibrous layer, which can also be described as a mesh.

In certain embodiments, the thermoplastic adhesive material will meet atleast one, or several, or all of the following parameters. An exemplarythermoplastic adhesive material may have a storage modulus G′ measuredat 20° C. of at least 30,000 Pa and less than 300,000 Pa, or less than200,000 Pa, or between 140,000 Pa and 200,000 Pa, or less than 100,000Pa. In a further aspect, the storage modulus G′ measured at 35° C. maybe greater than 80,000 Pa. In a further aspect, the storage modulus G′measured at 60° C. may be less than 300,000 Pa and more than 18,000 Pa,or more than 24,000 Pa, or more than 30,000 Pa, or more than 90,000 Pa.In a further aspect, the storage modulus G′ measured at 90° C. may beless than 200,000 Pa and more than 10,000 Pa, or more than 20,000 Pa, ormore then 30,000 Pa. The storage modulus measured at 60° C. and 90° C.may be a measure for the form stability of the thermoplastic adhesivematerial at elevated ambient temperatures. This value is particularlyimportant if the absorbent product is used in a hot climate where thethermoplastic adhesive material would lose its integrity if the storagemodulus G′ at 60° C. and 90° C. is not sufficiently high.

G′ can be measured using a rheometer as indicated in WO2010/27719. Therheometer is capable of applying a shear stress to the adhesive andmeasuring the resulting strain (shear deformation) response at constanttemperature. The adhesive is placed between a Peltier-element acting aslower, fixed plate and an upper plate with a radius R of e.g., 10 mm,which is connected to the drive shaft of a motor to generate the shearstress. The gap between both plates has a height H of e.g., 1500 micron.The Peltier-element enables temperature control of the material (+0.5°C.). The strain rate and frequency should be chosen such that allmeasurements are made in the linear viscoelastic region.

Absorbent Material Deposition Area 8

The absorbent core may comprise an absorbent material deposition area 8defined by the periphery of the layer formed by the absorbent material60 within the core wrap, as seen from the top when the absorbent core islaid flat, as illustrated in FIG. 3. The absorbent material 60 may beapplied continuously or discontinuously in the absorbent materialdeposition area 8. If absorbent material free channels or junction areasbetween pockets or stripes of absorbent material are present, these areconsidered to be part of the absorbent material deposition area 8, forexample for the purpose of measuring the width or the length L of theabsorbent material deposition area.

The shape of the absorbent material deposition area 8 can vary, inparticular it can be rectangular as shown in FIG. 3 or shaped with aso-called “dog bone” or “hour-glass” shape, which shows a tapering alongits width at least in the crotch region 81 of the absorbent materialdeposition area, as shown in FIG. 6. When shaped (non-rectangular), theabsorbent material deposition area 8 may have a relatively narrow widthin the crotch region 81 of the core as this may provide for examplebetter wearing comfort in the finished article incorporating the core.The absorbent material deposition area 8 may thus have a width (asmeasured in the transversal direction perpendicular to the longitudinalaxis 80′) at its narrowest point which is less than about 100 mm, 90 mm,80 mm, 70 mm, 60 mm or even less than about 50 mm. This narrowest widthmay typically be in the crotch region and may further be for example atleast 5 mm, or at least 10 mm, or at least 20 mm smaller than themaximum width of the absorbent material deposition area 8 at its largestpoint in the front region 82 and/or back region 83 of the absorbentcore.

The basis weight (amount deposited per unit of area) of the absorbentmaterial may also be varied along the absorbent material deposition area8 to create a profiled distribution of the absorbent material in thelongitudinal direction, in the transversal direction, or both directionsof the core. Hence the basis weight of the absorbent material may varyalong the longitudinal axis of the core 80′, as well as along thetransversal axis, or any axis parallel to any of these axes. The basisweight of absorbent material in area of relatively high basis weightsuch as the crotch point may thus be for example at least 10%, or 20%,or 30%, or 40%, or 50% higher than in an area of relatively low basisweight. In particular the absorbent material present in the absorbentmaterial deposition area 8 at the level of the crotch point C may havemore SAP per unit of area deposited as compared to any other area of thefront region 82 or back region 83 of the deposition area 8. The basisweight of the SAP may be at least 10%, or 20%, or 30%, or 40%, or 50%higher at the crotch point (C) of the core than at an another point ofthe absorbent material deposition area on the longitudinal axis, inparticular in the front or back region of the core.

The absorbent material 60 may be deposited using known techniques, whichmay allow relatively precise deposition of SAP at relatively high speed.In particular the SAP printing technology as disclosed for example inUS2006/24433 (Blessing), US2008/0312617 and US2010/0051166A1 (both toHundorf et al.) may be used. This technique uses a printing roll todeposit SAP onto a substrate disposed on a grid of a support which mayinclude a plurality of cross bars extending substantially parallel toand spaced from one another so as to form channels extending between theplurality of cross-bars. This technology allows high-speed and precisedeposition of SAP on a substrate. The channels of the absorbent core canbe formed for example by modifying the pattern of the grid and receivingdrums so that no SAP is applied in areas corresponding to the channels.EP application number 11169396.6 for example discloses this modificationin more details.

Superabsorbent Polymer (SAP)

“Superabsorbent polymers” (“SAP”) as used herein refer to absorbentmaterial which are cross-linked polymeric materials that can absorb atleast 10 times their weight of an aqueous 0.9% saline solution asmeasured using the Centrifuge Retention Capacity (CRC) test (EDANAmethod WSP 241.2-05E). The SAP of the invention may in particular have aCRC value of more than 20 g/g, or more than 24 g/g, or of from 20 to 50g/g, or from 20 to 40 g/g, or 24 to 30 g/g. The SAP useful in thepresent invention include a variety of water-insoluble, butwater-swellable polymers capable of absorbing large quantities offluids.

The superabsorbent polymer can be in particulate form so as to beflowable in the dry state. Typical particulate absorbent polymermaterials are made of poly(meth)acrylic acid polymers. However, e.g.starch-based particulate absorbent polymer material may also be used, aswell polyacrylamide copolymer, ethylene maleic anhydride copolymer,cross-linked carboxymethylcellulose, polyvinyl alcohol copolymers,cross-linked polyethylene oxide, and starch grafted copolymer ofpolyacrylonitrile. The superabsorbent polymer may be polyacrylates andpolyacrylic acid polymers that are internally and/or surfacecross-linked. Suitable materials are described in the PCT PatentApplication WO07/047598 or for example WO07/046052 or for exampleWO2009/155265 and WO2009/155264. In some embodiments, suitablesuperabsorbent polymer particles may be obtained by current state of theart production processes as is more particularly as described in WO2006/083584. The superabsorbent polymers are preferably internallycross-linked, i.e. the polymerization is carried out in the presence ofcompounds having two or more polymerizable groups which can befree-radically copolymerized into the polymer network. Usefulcrosslinkers include for example ethylene glycol dimethacrylate,diethylene glycol diacrylate, allyl methacrylate, trimethylolpropanetriacrylate, triallylamine, tetraallyloxyethane as described in EP-A 530438, di- and triacrylates as described in EP-A 547 847, EP-A 559 476,EP-A 632 068, WO 93/21237, WO 03/104299, WO 03/104300, WO 03/104301 andin DE-A 103 31 450, mixed acrylates which, as well as acrylate groups,include further ethylenically unsaturated groups, as described in DE-A103 31 456 and DE-A 103 55 401, or crosslinker mixtures as described forexample in DE-A 195 43 368, DE-A 196 46 484, WO 90/15830 and WO 02/32962as well as crosslinkers described in WO2009/155265. The superabsorbentpolymer particles may be externally surface cross-linked, or: postcross-linked). Useful post-crosslinkers include compounds including twoor more groups capable of forming covalent bonds with the carboxylategroups of the polymers. Useful compounds include for example alkoxysilylcompounds, polyaziridines, polyamines, polyamidoamines, di- orpolyglycidyl compounds as described in EP-A 083 022, EP-A 543 303 andEP-A 937 736, polyhydric alcohols as described in DE-C 33 14 019, cycliccarbonates as described in DE-A 40 20 780, 2-oxazolidone and itsderivatives, such as N-(2-hydroxyethyl)-2-oxazolidone as described inDE-A 198 07 502, bis- and poly-2-oxazolidones as described in DE-A 19807 992, 2-oxotetrahydro-1,3-oxazine and its derivatives as described inDE-A 198 54 573, N-acyl-2-oxazolidones as described in DE-A 198 54 574,cyclic ureas as described in DE-A 102 04 937, bicyclic amide acetals asdescribed in DE-A 103 34 584, oxetane and cyclic ureas as described inEP1,199,327 and morpholine-2,3-dione and its derivatives as described inWO03/031482.

In some embodiments, the SAP are formed from polyacrylic acidpolymers/polyacrylate polymers, for example having a neutralizationdegree of from 60% to 90%, or about 75%, having for example sodiumcounter ions.

The SAP useful for the present invention may be of numerous shapes. Theterm “particles” refers to granules, fibers, flakes, spheres, powders,platelets and other shapes and forms known to persons skilled in the artof superabsorbent polymer particles. In some embodiments, the SAPparticles can be in the shape of fibers, i.e. elongated, acicularsuperabsorbent polymer particles. In those embodiments, thesuperabsorbent polymer particles fibers have a minor dimension (i.e.diameter of the fiber) of less than about 1 mm, usually less than about500 μm, and preferably less than 250 μm down to 50 μm. The length of thefibers is preferably about 3 mm to about 100 mm. The fibers can also bein the form of a long filament that can be woven.

Typically, SAP are spherical-like particles. In contrast to fibers,“spherical-like particles” have a longest and a smallest dimension witha particulate ratio of longest to smallest particle dimension in therange of 1-5, where a value of 1 would equate a perfectly sphericalparticle and 5 would allow for some deviation from such a sphericalparticle. The superabsorbent polymer particles may have a particle sizeof less than 850 μm, or from 50 to 850 μm, preferably from 100 to 710μm, more preferably from 150 to 650 μm, as measured according to EDANAmethod WSP 220.2-05. SAP having a relatively low particle size help toincrease the surface area of the absorbent material which is in contactwith liquid exudates and therefore support fast absorption of liquidexudates.

The SAP may have a particle sizes in the range from 45 μm to 4000 μm,more specifically a particle size distribution within the range of from45 μm to about 2000 μm, or from about 100 μm to about 1000, 850 or 600μm. The particle size distribution of a material in particulate form canbe determined as it is known in the art, for example by means of drysieve analysis (EDANA 420.02 “Particle Size distribution).

In some embodiments herein, the superabsorbent material is in the formof particles with a mass medium particle size up to 2 mm, or between 50microns and 2 mm or to 1 mm, or preferably from 100 or 200 or 300 or 400or 500 μm, or to 1000 or to 800 or to 700 μm; as can for example bemeasured by the method set out in for example EP-A-0,691,133. In someembodiments of the invention, the superabsorbent polymer material is inthe form of particles whereof at least 80% by weight are particles of asize between 50 μm and 1200 μm and having a mass median particle sizebetween any of the range combinations above. In addition, or in anotherembodiment of the invention, said particles are essentially spherical.In yet another or additional embodiment of the invention thesuperabsorbent polymer material has a relatively narrow range ofparticle sizes, e.g. with the majority (e.g. at least 80% or preferablyat least 90% or even at least 95% by weight) of particles having aparticle size between 50 μm and 1000 μm, preferably between 100 μm and800 μm, and more preferably between 200 μm and 600 μm.

Suitable SAP may for example be obtained from inverse phase suspensionpolymerizations as described in U.S. Pat. Nos. 4,340,706 and 5,849,816or from spray- or other gas-phase dispersion polymerizations asdescribed in US Patent Applications No. 2009/0192035, 2009/0258994 and2010/0068520. In some embodiments, suitable SAP may be obtained bycurrent state of the art production processes as is more particularlydescribed from page 12, line 23 to page 20, line 27 of WO 2006/083584.

The surface of the SAP may be coated, for example, with a cationicpolymer. Preferred cationic polymers can include polyamine or polyiminematerials. In some embodiments, the SAP may be coated with chitosanmaterials such as those disclosed in U.S. Pat. No. 7,537,832. In someother embodiments, the SAP may comprise mixed-bed Ion-Exchange absorbentpolymers such as those disclosed in WO 99/34841 and WO 99/34842.

The absorbent core will typically comprise only one type of SAP, but itis not excluded that a blend of SAPs may be used. The fluid permeabilityof a superabsorbent polymer can be quantified using its UrinePermeability Measurement (UPM) value, as measured in the test disclosedEuropean patent application number EP12174117.7. The UPM of the SAP mayfor example be of at least 10×10⁻⁷ cm³·sec/g, or at least 30×10⁻⁷cm³·sec/g, or at least 50×10⁻⁷ cm³·sec/g, or more, e.g. at least 80 or100×10⁻⁷ cm³·sec/g. The flow characteristics can also be adjusted byvarying the quantity and distribution of the SAP used in the secondabsorbent layer.

For most absorbent articles, the liquid discharge occurs predominatelyin the front half of the article, in particular for diaper. Theabsorbent core may be thus placed in the absorbent article so that thefront half of the absorbent article comprises most of the absorbentcapacity of the core. Thus, at least: 60%, or 65%, or 70%, or 75%, or80% of the SAP by weight may be present in the front half of theabsorbent article, the remaining SAP being disposed in the back half ofthe absorbent article. The front half region of the absorbent articlecan be defined as the region between the front edge 10 of the absorbentarticle and the transversal axis 90 of the absorbent article. Thetransversal axis 90 is perpendicular to the longitudinal axis 80 andplaced at a distance of half the length of the article as measured onlongitudinal axis of the article from the front or back edge thereof.

The total amount of SAP present in the absorbent core may also varyaccording to expected user. Diapers for newborns may require less SAPthan infant or adult incontinence diapers. The amount of SAP in the coremay be for example comprised from about 5 to 60 g, in particular from 5to 50 g. The average SAP basis weight within the (or “at least one”, ifseveral are present) deposition area 8 of the SAP may be for example ofat least 50, 100, 200, 300, 400, 500 or more g/m². The areas of thechannels present in the absorbent material deposition area 8 are deducedfrom the absorbent material deposition area to calculate this averagebasis weight.

Core Wrap (16, 16′)

The core wrap may be made of a single substrate folded around theabsorbent material, or may advantageously comprise two (or more)substrates which are attached to another. Typical attachments are theso-called C-wrap and/or sandwich wrap. In a C-wrap, as exemplarily shownin FIGS. 2 and 4, the longitudinal and/or transversal edges of one ofthe substrate are folded over the other substrate to form flaps. Theseflaps are then bonded to the external surface of the other substrate,typically by gluing.

The core wrap may be formed by any materials suitable for receiving andcontaining the absorbent material. Typical substrate materials used inthe production of conventional cores may be used, in particular paper,tissues, films, wovens or nonwovens, or laminate of any of these. Thecore wrap may in particular be formed by a nonwoven web, such as acarded nonwoven, spunbond nonwoven (“S”) or meltblown nonwoven (“M”),and laminates of any of these. For example spunmelt polypropylenenonwovens are suitable, in particular those having a laminate web SMS,or SMMS, or SSMMS, structure, and having a basis weight range of about 5gsm to 15 gsm. Suitable materials are for example disclosed in U.S. Pat.No. 7,744,576, US2011/0268932A1, US2011/0319848A1 or US2011/0250413A1.Nonwoven materials provided from synthetic fibers may be used, such asPE, PET and in particular PP.

If the core wrap comprises a first substrate 16 and a second substrate16′ these may be made of the same type of material, or may be made ofdifferent materials or one of the substrate may be treated differentlythan the other to provide it with different properties. As the polymersused for nonwoven production are inherently hydrophobic, they arepreferably coated with hydrophilic coatings if placed on the fluidreceiving side of the absorbent core. It is advantageous that the topside of the core wrap, i.e. the side placed closer to the wearer in theabsorbent article, be more hydrophilic than the bottom side of the corewrap. A possible way to produce nonwovens with durably hydrophiliccoatings is via applying a hydrophilic monomer and a radicalpolymerization initiator onto the nonwoven, and conducting apolymerization activated via UV light resulting in monomer chemicallybound to the surface of the nonwoven. An alternative possible way toproduce nonwovens with durably hydrophilic coatings is to coat thenonwoven with hydrophilic nanoparticles, e.g. as described in WO02/064877.

Permanently hydrophilic nonwovens are also useful in some embodiments.Surface tension, as described in U.S. Pat. No. 7,744,576 (Busam et al.),can be used to measure how permanently a certain hydrophilicity level isachieved. Liquid strike through, as described in U.S. Pat. No.7,744,576, can be used to measure the hydrophilicity level. The firstand/or second substrate may in particular have a surface tension of atleast 55, preferably at least 60 and most preferably at least 65 mN/m orhigher when being wetted with saline solution. The substrate may alsohave a liquid strike through time of less than 5 s for a fifth gush ofliquid. These values can be measured using the test methods described inU.S. Pat. No. 7,744,576B2: “Determination Of Surface Tension” and“Determination of Strike Through” respectively.

Hydrophilicity and wettability are typically defined in terms of contactangle and the strike through time of the fluids, for example through anonwoven fabric. This is discussed in detail in the American ChemicalSociety publication entitled “Contact angle, wettability and adhesion”,edited by Robert F. Gould (Copyright 1964). A substrate having a lowercontact angle between the water and the surface of substrate may be saidto be more hydrophilic than another.

The substrates may also be air-permeable. Films useful herein maytherefore comprise micro-pores. The substrate may have for example anair-permeability of from 40 or from 50, to 300 or to 200 m³/(m²×min), asdetermined by EDANA method 140-1-99 (125 Pa, 38.3 cm²). The material ofthe core wrap may alternatively have a lower air-permeability, e.g.being non-air-permeable, for example to facilitate handling on a movingsurface comprising vacuum.

In the present invention, the core wrap may be at least partially sealedalong all the sides of the absorbent core or otherwise so thatsubstantially no absorbent material leaks out of the core wrap whileperforming the WCACF Test indicated below. By “substantially noabsorbent material” it is meant that less than 5%, advantageously lessthan 2%, or less than 1% or 0% by weight of absorbent material escapesthe core wrap. In particular the core wrap should not in an appreciableway burst open while the test is conducted.

The term “seal” is to be understood in a broad sense. The seal does notneed to be continuous along the whole periphery of the core wrap but maybe discontinuous along part or the whole of it, such as formed by aseries of closely spaced apart seal points on a line. While the seal maybe at the periphery of the core, it is not excluded that a seal may alsobe at other locations of the core, for example close to the longitudinalcenterline 80′. Typically a seal may be formed by gluing and/or thermalbonding.

If the core wrap is formed by two substrates 16, 16′, one seal per edgeof the core may be typically be used to enclose the absorbent material60 within the core wrap. This is exemplified in the FIGS. 4 and 5. Asshown in FIG. 4, for example, the first substrate 16 may be placed onone side of the core (the top side as represented therein) and extendsaround the core's longitudinal edges to at least partially wrap theopposed (bottom) side of the core. The second substrate 16′ can bepresent between the wrapped flaps of the first substrate 16 and theabsorbent material 60 of the core. The flaps of the first substrate 16may be glued to the second substrate 16′ to provide a strong seal. Thisso called C-wrap construction can provide benefits such as improvedresistance to bursting in a wet loaded state compared to a sandwichseal. The front edge and back edge of the core wrap may then also besealed for example by gluing the first substrate and second substrateflat to another to provide more complete enclosure of the absorbentmaterial across the whole of the periphery of the core. It can beadvantageous to use the C-wrap at least on the longitudinal edges of thecore which are longer than the front and end edges. In the so-calledsandwich construction, the first and second substrates may also extendoutwardly on all edges of the core and be sealed flat along the whole orparts of the periphery of the core typically by gluing and/orheat/pressure bonding. Typically neither first nor second substratesneed to be shaped, so that they can be rectangularly cut for ease ofproduction but of course other shapes are possible.

The core wrap may also be formed by a single substrate which may encloseas in a parcel wrap the absorbent material and be for example sealedalong the front edge and back edge of the core and one longitudinalseal.

Channels 26, 26′

The absorbent core comprises at least one channel which is at leastpartially oriented in the longitudinal direction of the core. If thefollowing the plural form “channels” will be used to mean “at least onechannel”. The channels may be formed in various ways. For example thechannels may be formed by zones within the absorbent material depositionarea which may be substantially or completely free of absorbentmaterial, in particular SAP. In addition or alternatively, thechannel(s) may also be formed by continuously or discontinuously bondingthe material forming the top side of the core wrap to the materialforming the bottom side of the core wrap through the absorbent materialdeposition area. The channels may be advantageously continuous but it isnot excluded that the channels are intermittent. Theacquisition-distribution system or any sub-layer between the topsheetand the absorbent core, or another layer of the article, may alsocomprise channels, which may or not correspond to the channels of theabsorbent core. The channels may be in particular fully encompassedwithin the absorbent material deposition area 8.

The channel or channels may in particular be present within the crotchregion (81) of the core, in particular at least at the same longitudinallevel as the crotch point C, as represented in FIG. 3 by the twolongitudinally extending channels 26, 26′. Some channels may also extendfrom the crotch region 81 into the back region 82 and/or front region 83of the core or may be solely present in the front region and/or in theback region of the core, as represented in FIG. 6 by the smallerchannels 27, 27′.

The absorbent core 28 may also comprise more than two channels, forexample at least 3, or at least 4 or at least 5 or at least 6. Shorterchannels may also be present, for example in the back region or thefront region of the core as represented by the pair of channels 27, 27′in FIG. 6 towards the front of the core. The channels may comprise oneor more pairs of channels symmetrically arranged relative to thelongitudinal axis 80′.

The channels may be particularly useful in the absorbent core when theabsorbent material deposition area is rectangular, as the channels canimprove the flexibility of the core to an extent that there is lessadvantage in using a non-rectangular (shaped) core. Of course channelsmay also be present in a layer of SAP having a shaped deposition area.

The channels may extend substantially longitudinally, which meanstypically that each channel extends more in the longitudinal directionthan in the transverse direction, and typically at least twice as muchin the longitudinal direction than in the transverse direction (asmeasured after projection on the respective axis). The channels may havea length L′ projected on the longitudinal axis 80′ of the core that isat least 10% of the length L of the absorbent material deposition area8. It may be advantageous that at least some or all of the channels arenot completely or substantially completely transversely orientedchannels in the core.

The channels may be completely oriented longitudinally and parallel tothe longitudinal axis but also may be curved. In particular some or allthe channels, in particular the channels present in the crotch region,may be concave towards the longitudinal axis 80′, as for examplerepresented in FIGS. 3 and 7 for the pair of channels 26, 26′. Theradius of curvature may typically be at least equal (and preferably atleast 1.5 or at least 2.0 times this average transverse dimension) tothe average transverse dimension of the absorbent material depositionarea 8; and also straight but under an angle of (e.g. from 5°) up to30°, or for example up to 20°, or up to 10° with a line parallel to thelongitudinal axis. The radius of curvature may be constant for achannel, or may vary along its length. This may also includes channelswith an angle therein, provided said angle between two parts of achannel is at least 120°, preferably at least 150°; and in any of thesecases, provided the longitudinal extension of the channel is more thanthe transverse extension. The channels may also be branched, for examplea central channel superposed with the longitudinal axis in the crotchregion which branches towards the back and/or towards the front of thearticle.

In some embodiments, there is no channel that coincides with thelongitudinal axis 80′ of the core. When present as symmetrical pairsrelative to the longitudinal axis, the channels may be spaced apart fromone another over their whole longitudinal dimension. The smallestspacing distance may be for example at least 5 mm, or at least 10 mm, orat least 16 mm.

Furthermore, in order to reduce the risk of fluid leakages, thelongitudinal main channels typically do not extend up to any of theedges of the absorbent material deposition area 8, and are thereforefully encompassed within the absorbent material deposition area of thecore. Typically, the smallest distance between a channel and the closestedge of the absorbent material deposition area is at least 5 mm.

The channels may have a width We along at least part of its length whichis at least 2 mm, or at least 3 mm or at least 4 mm, up to for example20 mm, or 16 mm or 12 mm. The width of the channel may be constantthrough substantially the whole length of the channel or may vary alongits length.

At least some or all the channels are advantageously permanent channels,meaning their integrity is at least partially maintained both in the drystate and in the wet state. Permanent channels may be obtained byprovision of one or more adhesive material, for example the fibrouslayer of adhesive material or a construction glue that helps adheringfor example a substrate with an absorbent material within the walls ofthe channel. Permanent channels may be also in particular formed bybonding the upper side and lower side of the core wrap (e.g. firstsubstrate 16 and the second substrate 16′) together through thechannels. Typically, an adhesive can be used to bond both sides of thecore wrap through the channels, but it is possible to bond via otherknown means, such as pressure bonding, ultrasonic bonding or heatbonding or combination thereof. The core wrap can be continuously bondedor intermittently bonded along the channels. The channels mayadvantageously remain or become visible at least through the topsheetand/or backsheet when the absorbent article is fully loaded with a fluidas disclosed in the Wet Channel Integrity Test below. This may beobtained by making the channels substantially free of SAP, so they willnot swell, and sufficiently large so that they will not close when wet.Furthermore bonding the core wrap to itself through the channels may beadvantageous. The Wet Channel Integrity Test described below can be usedto test if channels are permanent and visible following wet saturationand to what extent. Advantageously, a permanent channel according to theinvention has a percentage of integrity of at least: 20%, or 30%, or40%, or 50%, or 60, or 70%, or 80%, or 90%, according to the Wet Channel

Integrity Test described below.

Topsheet 24

The topsheet 24 is the part of the absorbent article that is directly incontact with the wearer's skin. The topsheet 24 can be joined to thebacksheet 25, the core 28 and/or any other layers as is known in the art(as used herein, the term “joined” encompasses configurations whereby anelement is directly secured to another element by affixing the elementdirectly to the other element, and configurations whereby an element isindirectly secured to another element by affixing the element tointermediate member(s) which in turn are affixed to the other element).Usually, the topsheet 24 and the backsheet 25 are joined directly toeach other in some locations (e.g. on or close to the periphery of thearticle) and are indirectly joined together in other locations bydirectly joining them to one or more other elements of the article 20.

The topsheet 24 is preferably compliant, soft-feeling, andnon-irritating to the wearer's skin. Further, at least a portion of thetopsheet 24 is liquid permeable, permitting liquids to readily penetratethrough its thickness. A suitable topsheet may be manufactured from awide range of materials, such as porous foams, reticulated foams,apertured plastic films, or woven or nonwoven materials of naturalfibers (e.g., wood or cotton fibers), synthetic fibers or filaments(e.g., polyester or polypropylene or bicomponent PE/PP fibers ormixtures thereof), or a combination of natural and synthetic fibers. Ifthe topsheet 24 includes fibers, the fibers may be spunbond, carded,wet-laid, meltblown, hydroentangled, or otherwise processed as is knownin the art, in particular spunbond PP nonwoven. A suitable topsheetcomprising a web of staple-length polypropylene fibers is manufacturedby Veratec, Inc., a Division of International Paper Company, of Walpole,Mass. under the designation P-8.

Suitable formed film topsheets are also described in U.S. Pat. Nos.3,929,135, 4,324,246, 4,342,314, 4,463,045, and 5,006,394. Othersuitable topsheets may be made in accordance with U.S. Pat. Nos.4,609,518 and 4,629,643 issued to Curro et al. Such formed films areavailable from The Procter & Gamble Company of Cincinnati, Ohio as“DRI-WEAVE” and from Tredegar Corporation, based in Richmond, Va., as“CLIFF-T”.

Any portion of the topsheet may be coated with a lotion as is known inthe art. Examples of suitable lotions include those described in U.S.Pat. Nos. 5,607,760, 5,609,587, 5,643,588, 5,968,025 and 6,716,441. Thetopsheet 24 may also include or be treated with antibacterial agents,some examples of which are disclosed in PCT Publication WO95/24173.Further, the topsheet, the backsheet or any portion of the topsheet orbacksheet may be embossed and/or matte finished to provide a more clothlike appearance.

The topsheet 24 may comprise one or more apertures to ease penetrationof exudates therethrough, such as urine and/or feces (solid, semi-solid,or liquid). The size of at least the primary aperture is important inachieving the desired waste encapsulation performance. If the primaryaperture is too small, the waste may not pass through the aperture,either due to poor alignment of the waste source and the aperturelocation or due to fecal masses having a diameter greater than theaperture. If the aperture is too large, the area of skin that may becontaminated by “rewet” from the article is increased. Typically, thetotal area of the apertures at the surface of a diaper may have an areaof between about 10 cm² and about 50 cm², in particular between about 15cm² and 35 cm². Examples of apertured topsheet are disclosed in U.S.Pat. No. 6,632,504, assigned to BBA NONWOVENS SIMPSONVILLE.WO2011/163582 also discloses suitable colored topsheet having a basisweight of from 12 to 18 gsm and comprising a plurality of bonded points.Each of the bonded points has a surface area of from 2 mm² to 5 mm² andthe cumulated surface area of the plurality of bonded points is from 10to 25% of the total surface area of the topsheet.

Typical diaper topsheets have a basis weight of from about 10 to about28 gsm, in particular between from about 12 to about 18 gsm but otherbasis weights are possible.

Backsheet 25

The backsheet 25 is generally that portion of the absorbent article 20which forms the majority of the external surface of the article whenworn by the user. The backsheet is positioned towards the bottom side ofthe absorbent core and prevents the exudates absorbed and containedtherein from soiling articles such as bedsheets and undergarments. Thebacksheet 25 is typically impermeable to liquids (e.g. urine). Thebacksheet may for example be or comprise a thin plastic film such as athermoplastic film having a thickness of about 0.012 mm to about 0.051mm. Exemplary backsheet films include those manufactured by TredegarCorporation, based in Richmond, Va., and sold under the trade name CPC2film. Other suitable backsheet materials may include breathablematerials which permit vapors to escape from the diaper 20 while stillpreventing exudates from passing through the backsheet 25. Exemplarybreathable materials may include materials such as woven webs, nonwovenwebs, composite materials such as film-coated nonwoven webs, microporousfilms such as manufactured by Mitsui Toatsu Co., of Japan under thedesignation ESPOIR NO and by Tredegar Corporation of Richmond, Va., andsold under the designation EXAIRE, and monolithic films such asmanufactured by Clopay Corporation, Cincinnati, Ohio under the nameHYTREL blend P18-3097. Some breathable composite materials are describedin greater detail in PCT Application No. WO 95/16746 published on Jun.22, 1995 in the name of E. I. DuPont; U.S. Pat. No. 5,938,648 to LaVonet al., U.S. Pat. No. 4,681,793 to Linman et al., U.S. Pat. No.5,865,823 to Curro; and U.S. Pat. No. 5,571,096 to Dobrin et al, U.S.Pat. No. 6,946,585B2 to London Brown.

The backsheet 25 may be joined to the topsheet 24, the absorbent core 28or any other element of the diaper 20 by any attachment means known inthe art. Suitable attachment means are described above with respect tomeans for joining the topsheet 24 to other elements of the article 20.For example, the attachment means may include a uniform continuous layerof adhesive, a patterned layer of adhesive, or an array of separatelines, spirals, or spots of adhesive. Suitable attachment meanscomprises an open pattern network of filaments of adhesive as disclosedin U.S. Pat. No. 4,573,986. Other suitable attachment means includeseveral lines of adhesive filaments which are swirled into a spiralpattern, as is illustrated by the apparatus and methods shown in U.S.Pat. Nos. 3,911,173, 4,785,996; and 4,842,666. Adhesives which have beenfound to be satisfactory are manufactured by H. B. Fuller Company of St.Paul, Minn. and marketed as HL-1620 and HL 1358-XZP. Alternatively, theattachment means may comprise heat bonds, pressure bonds, ultrasonicbonds, dynamic mechanical bonds, or any other suitable attachment meansor combinations of these attachment means as are known in the art.

Acquisition-Distribution System

The absorbent articles of the invention may comprise an acquisitionlayer 52, a distribution layer 54, or combination of both (all hereincollectively referred to as acquisition-distribution system “ADS”). Thefunction of the ADS is typically to quickly acquire the fluid anddistribute it to the absorbent core in an efficient manner. The ADS maycomprise one, two or more layers, which may form a unitary layer orremain discrete layers which may be attached to each other. In theexamples below, the ADS comprises two layers: a distribution layer 54and an acquisition layer 52 disposed between the absorbent core and thetopsheet, but the invention is not restricted to this example.

Typically, the ADS will not comprise SAP as this may slow theacquisition and distribution of the fluid. The prior art discloses manytype of acquisition-distribution system, see for example WO2000/59430(Daley), WO95/10996 (Richards), U.S. Pat. No. 5,700,254 (McDowall),WO02/067809 (Graef). The ADS may comprise, although not necessarily, twolayers: a distribution layer 54 and an acquisition layer 52, which willnow be exemplified in more details.

Distribution Layer 54

The function of a distribution layer 54 is to spread the insulting fluidliquid over a larger surface within the article so that the absorbentcapacity of the core can be more efficiently used. Typicallydistribution layer are made of a nonwoven material based on synthetic orcellulosic fibers and having a relatively low density. The density ofthe distribution layer may vary depending on the compression of thearticle, but may typically range from 0.03 to 0.25 g/cm³, in particularfrom 0.05 to 0.15 g/cm³ measured at 0.30 psi (2.07 kPa). Thedistribution layer 54 may also be a material having a water retentionvalue of from 25 to 60, preferably from 30 to 45, measured as indicatedin the procedure disclosed in U.S. Pat. No. 5,137,537. The distributionlayer may typically have an average basis weight of from 30 to 400 g/m²,in particular from 100 to 300 g/m².

The distribution layer may for example comprise at least 50% by weightof cross-linked cellulose fibers. The cross-linked cellulosic fibers maybe crimped, twisted, or curled, or a combination thereof includingcrimped, twisted, and curled. This type of material has been used in thepast in disposable diapers as part of an acquisition system, for exampleUS 2008/0312622 A1 (Hundorf). The cross-linked cellulosic fibers providehigher resilience and therefore higher resistance to the first absorbentlayer against the compression in the product packaging or in useconditions, e.g. under baby weight. This provides the core with a highervoid volume, permeability and liquid absorption, and hence reducedleakage and improved dryness.

Exemplary chemically cross-linked cellulosic fibers suitable for adistribution layer are disclosed in U.S. Pat. Nos. 5,549,791, 5,137,537,WO9534329 or US2007/118087. Exemplary cross-linking agents includepolycarboxylic acids such as citric acid and/or polyacrylic acids suchas acrylic acid and maleic acid copolymers. For example, the crosslinkedcellulosic fibers may have between about 0.5 mole % and about 10.0 mole% of a C2-C9 polycarboxylic acid cross-linking agent, calculated on acellulose anhydroglucose molar basis, reacted with said fibers in anintrafiber ester crosslink bond form. The C2-C9 polycarboxylic acidcross-linking agent may be selected from the group consisting of:

-   -   aliphatic and alicyclic C2-C9 polycarboxylic acids having at        least three carboxyl groups per molecule; and    -   aliphatic and alicyclic C2-C9 polycarboxylic acids having two        carboxyl groups per molecule and having a carbon-carbon double        bond located alpha, beta to one or both of the carboxyl groups,        wherein one carboxyl group in said C2-C9 polycarboxylic acid        crosslinking agent is separated from a second carboxyl group by        either two or three carbon atoms. The fibers may have in        particular between about 1.5 mole % and about 6.0 mole %        crosslinking agent, calculated on a cellulose anhydroglucose        molar basis, reacted therewith in the form of intrafiber ester        crosslink bonds. The cross-linking agent may be selected from        the group consisting of citric acid, 1, 2, 3, 4 butane        tetracarboxylic acid, and 1, 2, 3 propane tricarboxylic acid, in        particular citric acid.

Polyacrylic acid cross-linking agents may also be selected frompolyacrylic acid homopolymers, copolymers of acrylic acid, and mixturesthereof. The fibers may have between 1.0 weight % and 10.0 weight %,preferably between 3 weight % and 7 weight %, of these cross-linkingagents, calculated on a dry fiber weight basis, reacted therewith in theform of intra-fiber crosslink bonds. The cross-linking agent may be apolyacrylic acid polymer having a molecular weight of from 500 to40,000, preferably from 1,000 to 20,000. The polymeric polyacrylic acidcross-linking agent may be a copolymer of acrylic acid and maleic acid,in particular wherein the weight ratio of acrylic acid to maleic acid isfrom 10:1 to 1:1, preferably from 5:1 to 1.5:1. An effective amount ofcitric acid may be further mixed with said polymeric polyacrylic acidcross-linking agent.

The distribution layer comprising cross-linked cellulose fibers maycomprise other fibers, but this layer may advantageously comprise atleast 50%, or 60%, or 70%, or 80%, or 90% or even up to 100%, by weightof the layer, of cross-linked cellulose fibers (including thecross-linking agents). Examples of such mixed layer of cross-linkedcellulose fibers may comprise about 70% by weight of chemicallycross-linked cellulose fibers, about 10% by weight polyester (PET)fibers, and about 20% by weight untreated pulp fibers. In anotherexample, the layer of cross-linked cellulose fibers may comprise about70% by weight chemically cross-linked cellulose fibers, about 20% byweight lyocell fibers, and about 10% by weight PET fibers. In anotherexample, the layer may comprise about 68% by weight chemicallycross-linked cellulose fibers, about 16% by weight untreated pulpfibers, and about 16% by weight PET fibers. In another example, thelayer of cross-linked cellulose fibers may comprise from about 90-100%by weight chemically cross-linked cellulose fibers.

Acquisition Layer 52

The absorbent article 20 may comprise an acquisition layer 52, whosefunction is to quickly acquire the fluid away from the topsheet so as toprovide a good dryness for the wearer. The acquisition layer 52 istypically placed directly under the topsheet. If present, thedistribution layer may be at least partially disposed under theacquisition layer. The acquisition layer may typically be or comprise anon-woven material, for example a SMS or SMMS material, comprising aspunbonded, a melt-blown and a further spunbonded layer or alternativelya carded chemical-bonded nonwoven. The non-woven material may inparticular be latex bonded. Exemplary upper acquisition layers 52 aredisclosed in U.S. Pat. No. 7,786,341. Carded, resin-bonded nonwovens maybe used, in particular where the fibers used are solid round or roundand hollow PET staple fibers (50/50 or 40/60 mix of 6 denier and 9denier fibers). An exemplary binder is a butadiene/styrene latex.Non-wovens have the advantage that they can be manufactured outside theconverting line and stored and used as a roll of material.

Further useful non-wovens are described in U.S. Pat. No. 6,645,569 toCramer et al., U.S. Pat. No. 6,863,933 to Cramer et al., U.S. Pat. No.7,112,621 to Rohrbaugh et al., and co patent applications US2003/148684to Cramer et al. and US2005/008839 to Cramer et al.

The acquisition layer 52 may be stabilized by a latex binder, forexample a styrene-butadiene latex binder (SB latex). Processes forobtaining such lattices are known, for example, from EP 149 880 (Kwok)and US 2003/0105190 (Diehl et al.). In certain embodiments, the bindermay be present in the acquisition layer 52 in excess of about 12%, about14% or about 16% by weight. SB latex is available under the trade nameGENFLO™ 3160 (OMNOVA Solutions Inc.; Akron, Ohio).

A further acquisition layer may be used in addition to a firstacquisition layer described above. For example a tissue layer may beplaced between the first acquisition layer and the distribution layer.The tissue may have enhanced capillarity distribution propertiescompared to the acquisition layer described above. The tissue and thefirst acquisition layer may be of the same size or may be of differentsize, for example the tissue layer may extend further in the back of theabsorbent article than the first acquisition layer. An example ofhydrophilic tissue is a 13-15 gsm high wet strength made of cellulosefibers from supplier Havix.

Fastening System 42-44

The absorbent article may include a fastening system. The fasteningsystem can be used to provide lateral tensions about the circumferenceof the absorbent article to hold the absorbent article on the wearer.This fastening system is not necessary for training pant article sincethe waist region of these articles is already bonded. The fasteningsystem usually comprises a fastener such as tape tabs, hook and loopfastening components, interlocking fasteners such as tabs & slots,buckles, buttons, snaps, and/or hermaphroditic fastening components,although any other known fastening means are generally acceptable. Alanding zone is normally provided on the front waist region of thearticle for the fastener to be releasably attached. Some exemplarysurface fastening systems are disclosed in U.S. Pat. Nos. 3,848,594,4,662,875, 4,846,815, 4,894,060, 4,946,527, 5,151,092 and U.S. Pat. No.5,221,274 issued to Buell. An exemplary interlocking fastening system isdisclosed in U.S. Pat. No. 6,432,098. The fastening system may alsoprovide a means for holding the article in a disposal configuration asdisclosed in U.S. Pat. No. 4,963,140 issued to Robertson et al.

The fastening system may also include primary and secondary fasteningsystems, as disclosed in U.S. Pat. No. 4,699,622 to reduce shifting ofoverlapped portions or to improve fit as disclosed in U.S. Pat. Nos.5,242,436, 5,499,978, 5,507,736, and 5,591,152.

Front and Back Ears 46, 40

The absorbent article may comprise front ears 46 and back ears 40 as isknown in the art. The ears can be integral part of the chassis, forexample formed from the topsheet and/or backsheet as side panel.Alternatively, as represented on FIG. 1, they may be separate elementsattached by gluing and/or heat embossing. The back ears 40 areadvantageously stretchable to facilitate the attachment of the tabs 42on the landing zone 40 and maintain the taped diapers in place aroundthe wearer's waist. The back ears 40 may also be elastic or extensibleto provide a more comfortable and contouring fit by initiallyconformably fitting the absorbent article to the wearer and sustainingthis fit throughout the time of wear well past when absorbent articlehas been loaded with exudates since the elasticized ears allow the sidesof the absorbent article to expand and contract.

Barrier Leg Cuffs 34 and Gasketing Cuffs 32

Absorbent articles such as diapers or training pants may typicallyfurther comprise components that increase the fit of the article aroundthe legs of the wearer, in particular barrier leg cuffs 34 and gasketingcuffs 32. The barrier leg cuffs 32 may be formed by a piece of material,typically a nonwoven, which is partially bonded to the rest of thearticle and can be partially raised away and thus stand up from theplane defined by the topsheet, when the article is pulled flat as showne.g. in FIGS. 1-2. The barrier leg cuffs can provide improvedcontainment of liquids and other body exudates approximately at thejunction of the torso and legs of the wearer. The barrier leg cuffsextend at least partially between the front edge and the back edge ofthe absorbent article on opposite sides of the longitudinal axis and areat least present at the level of the crotch point (C).

The barrier leg cuffs may be delimited by a proximal edge 64 joined tothe rest of the article, typically the topsheet and/or the backsheet,and a free terminal edge 66, which is intended to contact and form aseal with the wearer's skin. The barrier leg cuffs 34 may be joined atthe proximal edge 64 with the chassis of the article by a bond 65 whichmay be made for example by gluing, fusion bonding or combination ofknown bonding means. The bond 65 at the proximal edge 64 may becontinuous or intermittent.

The barrier leg cuffs 32 can be integral with (i.e. formed from) thetopsheet or the backsheet, or more typically be formed from a separatematerial joined to the rest of the article. Typically the material ofthe barrier leg cuffs may extend through the whole length of the articlebut is “tack bonded” to the topsheet towards the front edge and backedge of the article so that in these sections the barrier leg cuffmaterial remains flush with the topsheet. Each barrier leg cuff 34 maycomprise one, two or more elastic strings 35 close to this free terminaledge 66 to provide a better seal.

In addition to the barrier leg cuffs 34, the article may comprisegasketing cuffs 32, which are formed in the same plane as the chassis ofabsorbent article, in particular may be at least partially enclosedbetween the topsheet and the backsheet, and may be placed transverselyoutwardly relative to the barrier leg cuffs. The gasketing cuffs canprovide a better seal around the thighs of the wearer. Usually eachgasketing leg cuff will comprise one or more elastic string or elasticelement comprised in the chassis of the diaper for example between thetopsheet and backsheet in the area of the leg openings.

U.S. Pat. No. 3,860,003 describes a disposable diaper which provides acontractible leg opening having a side flap and one or more elasticmembers to provide an elasticized leg cuff (a gasketing cuff). U.S. Pat.Nos. 4,808,178 and 4,909,803 issued to Aziz et al. describe disposablediapers having “stand-up” elasticized flaps (barrier leg cuffs) whichimprove the containment of the leg regions. U.S. Pat. Nos. 4,695,278 and4,795,454 issued to Lawson and to Dragoo respectively, describedisposable diapers having dual cuffs, including gasketing cuffs andbarrier leg cuffs. All or a portion of the barrier leg and/or gasketingcuffs may be treated with a lotion.

Elastic Waist Feature

The absorbent article may also comprise at least one elastic waistfeature (not represented) that helps to provide improved fit andcontainment. The elastic waist feature is generally intended toelastically expand and contract to dynamically fit the wearer's waist.The elastic waist feature preferably extends at least longitudinallyoutwardly from at least one waist edge of the absorbent core 28 andgenerally forms at least a portion of the back side of the absorbentarticle. Disposable diapers can be constructed so as to have two elasticwaist features, one positioned in the front waist region and onepositioned in the back waist region. The elastic waist feature may beconstructed in a number of different configurations including thosedescribed in U.S. Pat. Nos. 4,515,595, 4,710,189, 5,151,092 and5,221,274.

Relations Between the Layers and Components

Typically, adjacent layers will be joined together using conventionalbonding method such as adhesive coating via slot coating or spraying onthe whole or part of the surface of the layer, or thermo-bonding, orpressure bonding or combinations thereof. This bonding is notrepresented in the Figures (except for the bonding 65 between the raisedelement of the leg cuffs 34 with the topsheet 24) for clarity andreadability but bonding between the layers of the article should beconsidered to be present unless specifically excluded. Adhesives may betypically used to improve the adhesion of the different layers, forexample between the backsheet and the core wrap. The glue may be anystandard hotmelt glue as known in the art.

If an acquisition layer 52 is present, it may be advantageous that thisacquisition layer is larger than or least as large as the distributionlayer 54 in the longitudinal and/or transversal dimension. Thus thedistribution layer 54 can be deposited on the acquisition layer 52. Thissimplifies handling, in particular if the acquisition layer is anonwoven which can be unrolled from a roll of stock material. Thedistribution layer may also be deposited directly on the absorbentcore's upper side of the core wrap or another layer of the article.Also, an acquisition layer 52 larger than the distribution layer allowsto directly glue the acquisition layer to the storage core (at thelarger areas). This can provide an increased article integrity andbetter liquid communication.

The absorbent core and in particular its absorbent material depositionarea 8 may advantageously be at least as large and long andadvantageously at least partially larger and/or longer than any of thelayer in the ADS. This is because the absorbent material in the core canusually more effectively retain fluid and provide dryness benefitsacross a larger area than the ADS. The absorbent article may have arectangular SAP layer and a non-rectangular (shaped) ADS. The absorbentarticle may also have a rectangular (non-shaped) ADS and a rectangularlayer of SAP.

Method of Making

The absorbent cores and articles of the invention may be made by anyconventional methods known in the art. In particular the articles may behand-made or industrially produced at high speed on a modern convertingline.

Experimental Settings

The values indicated herein are measured according to the methodsindicated herein below, unless specified otherwise. All measurements areperformed at 21° C.±2° C. and 50%±20% RH, unless specified otherwise.All samples should be kept at least 24 hours in these conditions toequilibrate before conducting the tests, unless indicated otherwise. Allmeasurements should be reproduced on at least 4 samples and the averagevalue obtained indicated, unless otherwise indicated.

Centrifuge Retention Capacity (CRC)

The CRC measures the liquid absorbed by the superabsorbent polymerparticles for free swelling in excess liquid. The CRC is measuredaccording to EDANA method WSP 241.2-05.

Dry Absorbent Core Caliper Test

This test may be used to measure the caliper of the absorbent core(before use i.e. without fluid loading) in a standardized manner.

Equipment: Mitutoyo manual caliper gauge with a resolution of 0.01 mm—orequivalent instrument.

Contact Foot: Flat circular foot with a diameter of 17.0 mm (±0.2 mm). Acircular weight may be applied to the foot (e.g., a weight with a slotto facilitate application around the instrument shaft) to achieve thetarget weight. The total weight of foot and added weight (includingshaft) is selected to provide 2.07 kPa (0.30 psi) of pressure to thesample.

The caliper gauge is mounted with the lower surface of the contact footin an horizontal plane so that the lower surface of the contact footcontacts the center of the flat horizontal upper surface of a base plateapproximately 20×25 cm. The gauge is set to read zero with the contactfoot resting on the base plate.

Ruler: Calibrated metal ruler graduated in mm.

Stopwatch: Accuracy 1 second

Sample preparation: The core is conditioned at least 24 hours asindicated above.

Measurement procedure: The core is laid flat with the bottom side, i.e.the side intended to be placed towards the backsheet in the finishedarticle facing down. The point of measurement (e.g. the crotch point C)is carefully drawn on the top side of the core taking care not tocompress or deform the core.

The contact foot of the caliper gauge is raised and the core is placedflat on the base plate of the caliper gauge with the top side of thecore up so that when lowered, the center of the foot is on the markedmeasuring point.

The foot is gently lowered onto the article and released (ensurecalibration to “0” prior to the start of the measurement). The calipervalue is read to the nearest 0.01 mm, 10 seconds after the foot isreleased.

The procedure is repeated for each measuring point. If there is a foldat the measuring point, the measurement is done in the closest area tothis point but without any folds. Ten articles are measured in thismanner for a given product and the average caliper is calculated andreported with an accuracy of one tenth mm.

Absorbent Article Caliper Test

The Absorbent Article Caliper Test can be performed as for the DryAbsorbent Core Caliper Test with the difference that the caliper of thefinished absorbent article is measured instead of the caliper of thecore. The point of measurement may be the intersection of thelongitudinal axis (80) and transversal axis (90) of the absorbentarticle. If the absorbent articles were provided folded and/or in apackage, the articles to be measured are unfolded and/or removed fromthe center area of the package. If the package contains more than 4articles, the outer most two articles on each side of the package arenot used in the testing. If the package contains more than 4 but fewerthan 14 articles, then more than one package of articles is required tocomplete the testing. If the package contains 14 or more articles, thenonly one package of articles is required to perform the testing. If thepackage contains 4 or fewer articles then all articles in the packageare measured and multiple packages are required to perform themeasurement. Caliper readings should be taken 24±1 hours after thearticle is removed from the package, unfolded and conditioned. Physicalmanipulation of product should be minimal and restricted only tonecessary sample preparation.

Any elastic components of the article that prevent the article frombeing laid flat under the caliper foot are cut or removed. These mayinclude leg cuffs or waistbands. Pant-type articles are opened or cutalong the side seams as necessary. Apply sufficient tension to flattenout any folds/wrinkles. Care is taken to avoid touching and/orcompressing the area of measurement.

Wet Channel Integrity Test

This test is designed to check the integrity of a channel in anabsorbent core following wet saturation.

1. The full length (in millimeters) of the channel is measured in thedry state (if the channel is not straight, the curvilinear lengththrough the middle of the channel is measured).

2. The absorbent core is then completely immersed in a large excess(e.g. 5 liters) of synthetic urine “Saline”, with a concentration of9.00 g NaCl per 1000 ml solution prepared by dissolving the appropriateamount of sodium chloride in distilled water. The temperature of thesolution must be 20+/−5° C.

3. After 1 minute in the saline, the core is removed and held verticallyby one end for 5 seconds to drain, then extended flat on an horizontalsurface with the top side (the side intended to be facing the wearer inthe article) facing up. If the core comprises stretch elements, it ispulled taut so that no contraction is observed. The core can be fixed toan horizontal surface by clamps at its front edge and back edge, so thatno contraction can happen.

4. The absorbent core is covered with a rectangular suitably weightedrigid plate, with dimensions as follows: length equal to the full lengthof the core, and width equal to the maximum core width at the widestpoint.

5. A pressure of 18.0 kPa is applied for 30 seconds over the area of therigid plate above mentioned. Pressure is calculated on the basis ofoverall area encompassed by the rigid plate. Pressure is achieved byplacing additional weights in the geometric center of the rigid plate,such that the combined weight of the rigid plate and the additionalweights result in a pressure of 18.0 kPa over the total area of therigid plate.

6. After 30 seconds, the additional weights and the rigid plate areremoved.

7. Immediately afterwards, the cumulative length of the portions of thechannel which remained intact is measured (in millimeters; if thechannel is not straight, the curvilinear length through the middle ofthe channel is measured). If no portions of the channel remained intactthen the channel is not permanent.

The percentage of integrity of the permanent channel is calculated bydividing the cumulative length of the portions of the channel whichremained intact by the length of the channel in the dry state, and thenmultiplying the quotient by 100.

Wet Caliper And Compression Force (WCACF) Test

This test measures a) the percentage of increase in caliper of asaturated absorbent core following one lateral compression, and b) theforce required to laterally compress the saturated absorbent core to awidth of 40 mm. The WCACF Test is to be performed on an absorbent coreaccording to the following instructions.

-   -   1. Mark the longitudinal axis on the absorbent core on the top        side of the core. The longitudinal axis generally divides the        top side of the core into two roughly symmetric pieces along the        length of the absorbent core when the core is viewed from the        top as exemplarily shown on FIG. 3. The top side of the core is        the side intended to be placed towards the wearer-facing side of        the absorbent article. In doubt, the top side is normally more        hydrophilic than the bottom side. If the top side still cannot        be identified, the test is then conducted on an equal number of        cores on alternative sides and the results averaged. Marking can        be made with any pen taking care not to damage the core while        marking.    -   2. Mark the crotch line on the same side of the absorbent core        as the longitudinal centerline. The crotch line is perpendicular        to the longitudinal axis and crosses the longitudinal axis at a        distance equal to 45% of the length L of the absorbent core        (0.45 L). This distance is measured from the front side of the        absorbent core (see FIG. 3 for an exemplary illustration). The        front side of the absorbent core is the side of the core        intended to be placed towards the front of the absorbent        article. If the intended orientation of the core is not known,        the front edge is on the side of the core where the amount of        SAP is higher. If the front edge can still not be identified,        then half the samples can be tested with the distance starting        from one side and the other half with the distance starting from        the other side, and the results averaged. The intersection of        the crotch line and the longitudinal axis is the crotch point C.    -   3. The absorbent core is then immersed in a large excess, e.g. 5        l, of synthetic urine “Saline”, with a concentration of 9.00 g        NaCl per 1000 ml solution prepared by dissolving the appropriate        amount of sodium chloride in distilled water. The container must        be large enough to accommodate the core in a flat configuration.        The marked side of the core faces up during the immersion.    -   4. After 1 minute in the saline, the absorbent core is removed        and held vertically by the front side for 10 seconds to drain.    -   5. The absorbent core is left to equilibrate for 10 minutes by        pulling it flat on a horizontal surface, with the top side        facing down. Clamps placed on the front and back sides of the        core may be used to keep the loaded core flat.    -   6. The caliper of the loaded absorbent core before compression        is then measured at the crotch point and reported as Cinitial.        For this purpose, a presser foot with a diameter of 17.0 mm is        used, and a pressure of 2.07 kPa (0.30 psi) is applied. The        absorbent core is laid flat on a plexiglas plate the marked side        facing up, and the presser foot is gently lowered so that it is        centered on the crotch point C. The thickness Cinitial is        measured 30±2 seconds after initial contact between the foot and        the core and reported to the nearest 0.1 mm.    -   7. The loaded absorbent core with its top side facing up is then        fixed on a rigid-plastic cylinder as schematically represented        in FIG. 7. The cylinder 600 has a diameter d of 150 mm (+−1 mm).        The last 20.0 mm (+−0.5 mm) of the front edge 280 of the core 28        is first attached to the external surface of the cylinder        closest to the operator via a double sided tape previously        applied on the cylinder or other fastening means so that the        absorbent core can be securely and releasably attached to the        cylinder. The last 20.0 mm (+−0.5 mm) of the back edge 282 of        the core 28 is then attached at the diametrically opposed        external surface of the cylinder at a high sufficient for the        crotch point C to coincide with the central axis 610 of the        cylinder 600.    -   8. One understands that the cylinder needs to be sufficiently        high so that the back edge of the core can be attached to it.    -   9. The absorbent core is then laterally compressed as detailed        below. Compressive forces are applied to the absorbent core by        an assembly comprised of a pair of compression plates 630, 640,        which simulate the portion of the legs compressing the absorbent        core during use. Each compression plate should have dimensions        90 mm (+−1 mm)×90 mm (+−1 mm). The plates can be made from any        suitable material that can be formed into the required flat,        square shape (e.g. aluminum, Plexiglas). The plates should be        placed lined up opposite one another. The compression plates are        placed so that the Crotch Line on the top side of the core and        the geometrical center of each compression plate are aligned and        are in a horizontal plane.    -   10. Each compression plate is driven toward the crotch point at        constant rate of 100 mm/min. (total closing speed is 200        mm/min). The gap between both compression plates starts at a        distance of 140.0 mm+−0.5 mm, or more if the width of the core        so requires, and then narrows to a final gap of 40.0 mm+−0.5 mm        when the absorbent core is compressed. The compression plates        may for example use an apparatus such as a Zwick Z 1.0 or        similar. The testing instrument includes a right clamp for        securing one compression plate, and a left clamp for securing        another compression plate. The equipment should include a force        cell with an appropriate measurement range e.g. up to 100 N and        a precision of at least +/−0.01 N.    -   11. Once the absorbent core has been compressed to 40 mm,        compression is maintained for 30 seconds. The force at the end        of the 30 seconds immediately before the compression is released        is recorded to the nearest 0.01 N and reported as the “Wet        Compression Force”. The compression plates can then be returned        to their initial positions at a speed of 100 mm/min for each        plate.    -   12. Immediately afterwards, the absorbent core is removed from        the cylinder 600, taking care to not touch the area that has        been compressed. If some absorbent material leaked out of the        core wrap during the compression step this leaked out absorbent        material is collected and weighted.    -   13. The caliper at the crotch point C is measured again using        the thickness measuring procedure as described above on step 6.        This caliper value is reported as Cfinal.

This procedure is repeated for at least 4 core samples. The Relative WetCaliper Increase (RWCI) of the absorbent core is then calculated asfollows:

Relative Wet Caliper Increase (%)=(ΣCfinal−ΣCinitial)*100/ΣCinitial

where ΣCfinal is the sum of Cfinal values measured for all the samplesand ΣCinitial is the sum of the Cinitial values measured for all thesamples. The Relative Wet Caliper Increase value of the cores accordingto the invention is less than 10.0%, in particular it may range of from1.0% to 9.5%, or 2.0% to 9.0%, or from to 2.5% to 8.0%.

If some absorbent material leaked at step 12, the rest of the absorbentmaterial still contained in the core can be extracted and also weighted.If the amount that leaked represents less than 5% by weight of the totalabsorbent material of the core (leaked and extracted) then it isconsidered that “substantially no absorbent material” leaked during thetest. Advantageously less than 2%, or less than 1% or even 0% by weightof absorbent material escapes the core wrap during step 12. Inparticular the core wrap should not in an appreciable way burst openwhile the test is conducted.

EXPERIMENTALS

The following absorbent core according to the invention was prepared:

Invention Example 1

The absorbent cores tested in this example were similar to the coreillustrated in FIG. 3. The cores contained SAP as absorbent material,without cellulosic fibers. The core wrap comprised two substratesforming the top and bottom sides of the core, the upper substrateforming a C-wrap along the longitudinal edges of the core and the frontand back edges of the core being attached flat. The core comprised twoabsorbent material free channels in the crotch region. The channels weresymmetric in relation to the longitudinal axis 80 had a projected lengththereon of about 227 mm, a width of about 8 mm and a shortest distancefrom each other of 20 mm. The core wrap was further attached to itselfthrough the channels.

The absorbent core comprised in total 14.1 g fast absorbing SAP appliedin an area of deposition having a length of 360 mm and a width of 110 mm(rectangular profile). The SAP was distributed so that the basis weightof SAP was higher in the crotch region than at the front region andstill lower towards the back region. There was no profiling of the SAPin the transversal direction (“cross-machine direction” or “CD”, exceptof the channels which were free of absorbent material). The absorbentcore was formed by SAP printing technology, as disclosed inUS2010/0051166A1, which combines two nonwoven substrates each supportinga SAP layer and having a microfiber elastic glue applied on each SAPlayer which immobilizes the SAP layer on the substrate. The channelswere formed by using a suitable printing drum delimiting the channelsshape, further information on how to form channels can be found in EPapplication number EP12174117.7 using printed SAP technology.

Auxiliary glue was applied between the SAP layer and the upper substrate16, and was slot coated with 41 slots 1 mm wide with a distance of 1 mmbetween the slots along the whole length of the core wrap (390 mm).0.211 g and 0.168 g of microfiber glue (from H. B. Fuller) wererespectively applied on the upper and lower SAP layer, the area ofapplication having a width of 110 mm and length of 390 mm on each SAPlayer.

The core wrap had a length of 390 mm with two end flaps free ofabsorbent material having a length of 15 mm at the back and at the frontedge of the absorbent core. The front and back end seals of the corewere slot glued together, the glue slots having a length of 30 mm fromthe front end seal and 20 mm from the back end seal. The folded width ofthe core wrap was 120 mm.

The upper substrate 16 was a 10 gsm hydrophilically treated SMMSnonwoven and the lower substrate 16′ was a 10 gsm SMMS nonwoven. Theupper substrate was cut at a length of 390 mm and a cut width of 165 mm.The lower substrate had a cut length of 390 mm and a cut width of 130mm. The upper substrate was C-wrapped around the lower substrate on thelateral edges of the core and the lateral edges of the lower layer wasslightly formed upwards on the edge of the absorbent material of thecore so that the overall width of the folded core wrap was about 120 mm.The C-wrap was made permanent by application between the substrates of acore folding glue applied at 20 gsm with 2 slots having a slot width of3 mm and 390 mm long on each side of the core.

The two substrates were additionally bonded together through thechannels. The bond was formed by applying pressure and the auxiliary andmicrofiber glue. The bond was strong. The core wrap seals resistedcompression and no absorbent material escaped the core wrap during theWCACF Test.

Invention Example 2

The cores tested in this example had two pair of channels and a shapeddeposition area similar to the one shown in FIG. 6. The width of theabsorbent material deposition area was 110 mm at the front and the backregion and 90 mm at the crotch point of the absorbent materialdeposition area.

The projected lengths of the long and short channels on the longitudinalaxis of the core were about 170 mm and 40 mm respectively. The smallestdistance between the longer channels was about 16 mm. The smallestdistance between the shorter channels was about 14 mm. The corescomprised 11.53 g of SAP. The core wrap comprised two nonwovens, the topsubstrate (16) was a 10 gsm SMMS nonwoven treated by a surfactant to behydrophilic. The lower substrate (16′) was a 11 gsm SMMS nonwoven.Auxiliary glue was applied between the lower SAP layer and itsrespective lower substrate which was slot coated with 41 slots 1 mm widewith a distance of 1 mm between the slots along the whole length of thecore wrap (390 mm). The microfiber glue (from H. B. Fuller) applied oneach SAP layer was uniformly applied at width of 108 mm and length of390 mm on each SAP layer, 0.211 g of microfiber glue was used on thecore cover side and 0.211 g on the dusting layer side. The rest of thecore construction was substantially similar as the cores in InventionExample 1.

Comparative Example

The comparative example 1 was substantially similar to Invention Example2 with the difference that the absorbent core did not comprise materialfree channels.

Test Results

Four samples of each above mentioned products were tested according tothe WCACF Test described above to measure the Relative Wet CaliperIncrease and the Wet Compression Force of the core. The averaged resultsare compiled below:

Relative wet Wet ΣCinitial/4 ΣCfinal/4 caliper Compression [mm] [mm]increase Force (N) Invention Example 1 13.0 13.8 6.2% 4.83 InventionExample 2 10.8 11.5 6.5% 2.81 Comparative 10.8 11.9 10.2% 3.05 example 1

DISCUSSION

While not wishing to be bound by theory it is believed that thefollowing features can provide alone or in combinations an increase inthe relative wet caliper to an absorbent core missing one or more of thebelow features. None of these features should be considered as beinglimited the scope of the claims, unless specifically claimed.

-   -   1) The top side of the wrap and the bottom side of the wrap may        advantageously be at least partially bonded to each other        through the channels. These bonds may be continuous or        intermittent, and may be made via gluing and/or heat bonding,        and may advantageously be sufficiently strong to at least        partially resist delamination upon fluid loading (“permanent        channels”), as discussed above. By constraining the core wrap in        the channels, these bonds increase the strain of the core wrap        and can diminish the wet caliper increase upon core loading.    -   2) The core wrap may comprise a first substrate (16) and a        second substrate (16′), both typically made of a nonwoven,        wherein the first substrate forms a C-wrap around the second        substrate. The first substrate may form the top side of the core        wrap and the second substrate may form at least part of the        bottom side of the core wrap. Typically the substrates may be        bonded, for example by gluing, along the wrapped flaps of the        first substrate together with the bottom side of the second        substrate. The inventors believe that a C-wrap, especially along        part or whole of the longitudinal sides of the absorbent core,        can better restrain the absorbent material from breaking out of        the core upon compression.    -   3) The Wet Compression Force is influenced by the amount of        absorbent material and the shape of the deposition area of the        core in the crotch region. It is believed that a lower amount of        absorbent material and/or a narrower deposition area at the        crotch region of the core (as in a shaped area) can provide a        decreased Wet Compression Force. The absorbent core of the        invention may exemplarily have a Wet Compression Force below        5.00 N, in particular less than 3.00 N, or from 1.00 N to 5.00        N, as measured by the WCACF Test.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. An absorbent core, wherein the absorbent corecomprises a core wrap enclosing an absorbent material; a front edge, aback edge, two longitudinal edges, a front region, a back region and acrotch region, the absorbent core having a longitudinal axis oriented ina longitudinal direction, and a length (L) as measured between the frontedge and back edge along the longitudinal axis which is at least 320 mm;a channel that is substantially free of the absorbent material, thatextends from the crotch region into the back region, and that is notcoincident with the longitudinal axis; wherein the absorbent core has aWet Compression Force of about 5.0 N or less; and wherein the core wrapis at least partially sealed along the edges of the core.
 2. Theabsorbent core of claim 1, wherein the channel has a length that is atleast 10% of the length L of the absorbent core.
 3. The absorbent coreaccording claim 1, wherein the channel comprises a width of at leastabout 2 mm.
 4. The absorbent core of claim 1, wherein the absorbentmaterial comprises less than about 10% of natural or synthetic fibers bytotal weight of the absorbent material.
 5. The absorbent core of claim1, wherein the first substrate comprises a first nonwoven and the secondsubstrate comprises a second nonwoven, and wherein the first nonwovenforms a C-wrap around the second nonwoven.
 6. The absorbent core ofclaim 1, wherein the absorbent material defines an absorbent materialdeposition area within the core wrap, wherein the absorbent materialdeposition area is rectangular or shaped with a width having a minimumin the crotch region.
 7. The absorbent core of claim 6, wherein thebasis weight of the superabsorbent polymers is not homogenouslydistributed along the longitudinal axis of the core, and wherein thebasis weight of the superabsorbent polymers is at least 10% percenthigher at the crotch point of the core than at another point of theabsorbent material deposition area on the longitudinal axis.
 8. Theabsorbent core of claim 1 wherein the absorbent material is at leastpartially immobilized on the core wrap.
 9. The absorbent core of claim 1comprising a first absorbent layer and a second absorbent layer, whereinthe first absorbent layer comprises a first substrate and a first layerof superabsorbent polymers, wherein the second absorbent layer comprisesa second substrate and a second layer of superabsorbent polymers. 10.The absorbent core of claim 1 wherein the Wet Compression Force fromabout 1.00 N to about 3.00 N.
 11. The absorbent core of claim 1,comprising from about 5 g to about 60 g of superabsorbent polymers. 12.The absorbent core of claim 1, wherein the caliper of the core, asmeasured at the crotch point, is from about 0.25 mm to about 5.0 mm. 13.An absorbent article comprising: a liquid permeable topsheet, a liquidimpermeable backsheet, and an absorbent core positioned between thetopsheet and the backsheet; wherein the absorbent core comprises theabsorbent core of claim
 1. 14. An absorbent core, wherein the absorbentcore comprises a core wrap enclosing an absorbent material; theabsorbent core comprising a front edge, a back edge, two longitudinaledges, a front region, a back region and a crotch region, the absorbentcore having a longitudinal axis oriented in a longitudinal direction,and a length (L) as measured between the front edge and back edge alongthe longitudinal axis which is at least 320 mm; a channel that issubstantially free of the absorbent material, that extends from thecrotch region into the back region, and that is not coincident with thelongitudinal axis; wherein the absorbent core has a Relative Wet CaliperIncrease (RWCI) after compression of less than 10.0%; and wherein thecore wrap is at least partially sealed along the edges of the core. 15.The absorbent core of claim 14, wherein the absorbent material comprisesat least about 90% of the superabsorbent polymers by total weight of theabsorbent material.
 16. The absorbent core of claim 14, wherein theabsorbent material is substantially free of natural or synthetic fibers.17. The absorbent core of claim 14, comprising from about 5 g to about60 g of superabsorbent polymers.
 18. The absorbent core of claim 14,wherein the caliper of the core, as measured at the crotch point, isfrom about 0.25 mm to about 5.0 mm.
 19. The absorbent core of claim 14further comprising a Wet Compression Force of about 5 N or less.
 20. Anabsorbent article comprising: a liquid permeable topsheet, a liquidimpermeable backsheet, and an absorbent core positioned between thetopsheet and the backsheet; wherein the absorbent core comprises theabsorbent core of claim 14.